Fuel cells, such as PEM fuel cells, use a simple chemical reaction to combine hydrogen and oxygen into water, producing electric current in the process. Traditionally, hydrogen may be produced by a chemical reaction between a fuel, such as lithium aluminum hydride, and water vapor. At an anode, hydrogen molecules are ionized by a platinum catalyst, and give up electrons. The proton exchange membrane (PEM) allows protons to flow through, but not electrons. As a result, hydrogen ions flow through the PEM to a cathode, while electrons flow through an external circuit. As the electrons travel through the external circuit, they can perform useful work by powering an electrical device such as an electric motor, light bulb or electronic circuitry. At the cathode, the electrons and hydrogen ions combine with oxygen to form water. The byproducts of the reaction are water and heat.
Fuels currently used in power generators, such as metal hydrides, have poor energy density. Pure alkali metals used as a fuel may theoretically improve the energy density of the fuel, but are pyrophoric and difficult to handle and store. Traditional fuels require high volume and/or high maintenance storage vessels which may also be a safety concern in many applications.